1. Field of The Invention
The present invention relates to a joint for an articulated ladder, and particularly to an arched lock piece disposed in the joint.
2. Description of Related Art
Due to a plurality of joints being mounted, an articulated ladder can be operated conveniently to obtain different preset angles among the ladder sections thereof. Conventionally, each of the joints has a positioning lock device therein so that a reliable operation of the articulated ladder can be achieved securely. However, many types of positioning lock devices have been developed so that each lock device makes the corresponding joint have its own way of operation.
The joint for an articulated ladder of the present invention is derived from German Utility Model No. 29600583.5 and U.S. Pat. No. 5,992,566, that is, the joint of the present invention is an improvement on German Utility Model No. 29600583.5 and U.S. Pat. No. 5,992,566. The German Utility Model No. 29600583.5 provides two inner casing parts with three locating recesses thereon respectively. Each of the locating recesses corresponding to a locating pin associated with an extension spring to constitute a catch device such that a trigger can be actuated to move a lock block in one of the locating recesses in case of the joint being operated to fold or to expand the articulated ladder. The catch device composed of three locating pins and three extension springs is attached in the inner casing parts so that it is quite sophisticated from the standpoint of the assembling job. Further, each extension spring at an end thereof is attached to the respective locating pin and at the other end thereof is attached to one of the inner casing parts so that it may cause a problem of jamming once the respective locating pin is subjected to an unbalanced pulling force of the respective extension spring.
The U.S. Pat. No. 5,992,566 provides two embodiments and one of the embodiments is characterized in that the catch device is composed of an arched block with three locating through holes, three locating pins, and an extension spring. Another embodiment of the U.S. Pat. No. 5,992,566 is characterized in that the catch device is composed of an arched block integral with three pairs of circular projections, and an extension spring. The catch device disclosed in the U.S. Pat. No. 5,992,566 is much simpler than that disclosed in the German Utility No. 29600583.5 for the assembling job. In addition, the U.S. Pat. No. 5,992,566 provides only one spring to move the arched block so that it is much more steady for the arched block during moving.
However, it is a problem that to fabricate the arched block disclosed in the U.S. Pat. No. 5,992,566 accurately takes more time and much more costly. The present inventor has endeavored to overcome the problem and discloses the present invention.
An object of the present invention is to provide a joint for an articulated ladder, which comprises an arched ring plate integral with three drawn short posts to be simply made and to perform a better function of catch device.